Infinitesimal in size, infinite in potential

Two Lehigh physicists have made significant artistic and scholarly contributions to a special issue on nanocarbon materials that was published recently by an international magazine.

Slava V. Rotkin and Tetyana Ignatova produced the cover illustration for the fall 2013 issue of Interface, the journal of the Electrochemical Society (ECS), and contributed a review article about the history, unique versatility and potential of nanocarbons.

In bold shades of blue, green and red, the cover image shows a nanotube interface in nanocarbon solar cells, a forest of nanotubes on a quartz substrate where heat conductance takes place, and T- and H-junctions formed by single-walled nanotubes functioning as electron splitters.

Rotkin, an associate professor of physics, and Ignatova, a Ph.D. candidate, generated 3-D graphics for the image. Monica Shell ’14, a design major, completed the design and coloring of the image under the supervision of Johanna Brams, a senior instructional technologist with library and technology services.

The issue of Interface is titled “New Frontiers in Nanocarbons.” The invited article by Rotkin and Ignatova, one of four in the issue, is titled “Discovering Properties of Nanocarbon Materials as a Pivot for Device Applications.”

Nanotechnology scientists, the two Lehigh physicists said, have achieved an unprecedented level of research productivity in the last two decades thanks to the unique properties of nanocarbon materials.

“It is rare in the history of modern science that a single area will be so productive for both fundamental research and its applications as the field of nanocarbon materials,” they wrote.

Since the discovery of carbon nanotubes in 1991, they said, 140,000 papers have been published by nanotechnology researchers in physics, materials science, chemistry and other fields. Two Nobel prizes have been awarded to nanotechnology researchers—one in chemistry (1996) and one in physics (2010)—in addition to the Nanotechnology Kavli prize in 2012.

Diverse shapes and applications

Nanotechnology has been defined as the engineering of systems with dimensions smaller than 100 nanometers. One nanometer (1 nm) equals one billionth of a meter or, as one wag put it, the length a man’s beard grows as he lifts his razor to his face.

Nanocarbons come in a variety of shapes and geometries, ranging from nanoparticles, nanowires and nanotubes to graphene—a crystalline lattice of interlocking hexagons—and fullerenes, which are hollow spherical molecules named for the American architect Buckminster Fuller, who invented the geodesic domes that the molecules resemble.

Nanocarbons’ special properties, said Rotkin and Ignatova, include a high level of mechanical stability and stiffness and unusual interfacial thermal conductance and optical performance. Particularly striking is the unprecedented strength of nanomaterials no more than a layer of atoms thick.

Those properties have opened up applications for nanocarbons in photovoltaic cells, liquid crystal devices, batteries and supercapacitors, electron field emitters and other electronic devices. Nanocarbons are also used as fillers in automobile tires, tennis rackets and other products.

A multifaceted research effort

Rotkin and his students, often collaborating with researchers from other disciplines, have received funding from the National Science Foundation and other agencies for a variety of nanocarbon projects. With Anand Jagota, professor of chemical engineering and director of Lehigh’s bioengineering program, Rotkin has investigated the wrapping of nanotubes (NT) with DNA strands in an effort to make it easier to manipulate the tubes in solution.

Ignatova, an experimental physicist, is working on the nanophysics fundamentals of the interactions of tubes with DNA and Rare Earth (RE) ions. Magnetic RE ions are the same particles that are routinely injected into the blood to do magnetic resonance imaging and are also used as biology optical markers, based on the physical effect of their photoluminescence. Ignatova studies the interaction of photoluminescent RE ions with DNA-wrapped NT hybrids. By looking at how the brightness of RE light emission disappears, the physicists were able to deduce the details of molecular “drama,” or the attraction or repulsion between DNA and RE, at distances that cannot be resolved by microscopy.

Ignatova and Rotkin discussed the potential relevance of this effect for biological or medical applications in their review article, as well as in a recent chapter of the Handbook on Carbon Nano Materials (World Scientific, 2012) that they co-wrote with Andrei M. Nemilentsau, a postdoctoral researcher in the physics department.

This study found a new twist in a collaboration with the Los Alamos National Laboratory (LANL). This project, supported by a LANL grant, focuses on gel-like materials that mimic the environment inside the body or living cell. The group, led by Stephen K. Doorn, a science partner leader at LANL, has discovered a method of producing silica gels embedded with nanotubes.

Ignatova and Michael Blades ’12, a graduate student, study RE ions in gels and their interaction at the nanoscale with water, DNA and other molecules. The project is funded by NSF.

“This is a complicated, multifaceted system,” says Rotkin. “Each element is relatively well-understood, but if you mix them together, you can’t predict how the system is going to behave.

“For example, in Michael’s experimental project, we saw RE move through the solution or gel much faster than predicted by a simple model. The motion of RE in solution is similar to the diffusion of a fragrance from an open vial. But in our observation, it was as if you instantaneously smelled the perfume across a street after the vial had been broken. We have no theoretical explanation yet for this effect.”

Andrei Nemilentsau, a postdoctoral research associate, studies quantum heat transfer across the interfaces of nanocarbon materials. The study is supported by the Air Force Office of Scientific Research. “In the quantum world,” says Rotkin, “counterintuitive things happen. We are studying how heat can jump across the air gaps, which is how photons can tunnel from nanocarbon materials.”

Dan You, a graduate student, is working with Nemilentsau to try to explain this quantum phenomenon.

Rotkin was elected secretary of ECS’s Nanocarbons Division in 2012. He is spending the fall semester on sabbatical as a visiting researcher at the University of Aachen’s Rheinisch-Westfälische Technische Hochschule in Germany, where he is studying graphene in magnetic fields at temperatures close to absolute zero. He will take a similar appointment in the spring at Sungkyunkwan University in Seoul, South Korea, to advance the field of nanocarbon devices.